SYSTEMATIC ACCOUNT 233 



covery Reports, vols I, ill and IV, where full particulars of locality, etc., will be found. 

 The numbers of the stations taken by the ' Discovery II ' are in sequence with those of 

 the 'Discovery' and no letters are prefixed to them. Those taken by the 'William 

 Scoresby ' are distinguished by the letters WS, those taken in the Ross Sea by the 

 'C. A. Larsen' by RS, and those taken at the Marine Biological Station at South 

 Georgia by MS. 



ALGAE 



Class BACILLARIOPHYCEAE 



Order BACILLARIALES 

 Suborder DISCINEAE 



Family COSCINODISCACEAE 

 Subfamily MELOSIROIDEAE 



1 . Cells in stiff chains, valve surface radially striate and furrowed ... ... ... Melosira 



2. Cells solitary, valve surface radially striate, striation fine, central umbilical scar ...Hyalodiscus 



Subfamily SKELETONEMOIDEAE 



1. Valve surface areolate, marginal spines unite cells into chains, intracellular distance 

 short ... ... ... ... ... ... ... ... ... ... Stephanopyxis 



2. Valve surface hyaline, marginal spines long, intracellular distance long ... Skeletonema 



3. Valve surface hyaline, marginal spines short, denticulate, valve surfaces contiguous ... Detomda 



Subfamily THALASSIOSIROIDEAE 



1 . Cells in mucous colonies, or in chains, united by a single thread, cells distant . . . Thalassiosira 



2. Cells united by numerous mucous threads ... ... ... ... ... Coscinoscira 



3. Cells united in chains, valves contiguous or nearly so, one marginal apicule... ... Lauderia 



4. Cells united by marginal spinulae, each spinule producing 2 mucous threads, valve centre 

 depressed, small central spine ... ... ... ... ... ... ... Schroderella 



Subfamily COSCINODISCOIDEAE 



1. Cells solitary, striation fasciculate, marginal ocellus ... ... ... ... Actinocyclus 



2. Marginal ocellus absent, valve surface areolate, peripheral extensions loculate 



Planktoniella 



3. Valve surface hyaline, peripheral extensions spinous ... ... ... ... Gossleriella 



4. Valves dissimilar, radially striate, one margin simple, the other striate ... ... Charcotia 



5. Valves dissimilar, striation fasciculate, one margin loculate, the other striate . . . Schimperiella 



6. Valves similar, diameter of cell greater than pervalvar axis, valve surface punctate or 

 areolate ... ... ... ... ... ... ... ... ... ... Coscinodiscus 



7. Diameter of cell less than pervalvar axis, valve surface punctate ... ... Ethmodiscus 



